Pathogenesis of symptoms in prostatic hyperplasia
For a deep understanding of the pharmacology of antiandrogen agents, it is necessary to clearly understand the pathogenesis of the conditions for which they are prescribed. Benign prostatic hyperplasia (BPH) is accompanied by a gradual increase in the size of the organ.
Since the prostate gland anatomically surrounds the prostatic urethra, its excessive growth inevitably leads to narrowing of the urinary tract lumen. As a result of this mechanical compression, the main clinical manifestation of the disease develops—persistent urinary retention. Therapeutic strategies for this condition are aimed either at relaxing the muscles surrounding the urethra or directly reducing the volume of hyperplastic tissue.
Classification of antiandrogen drugs
Antiandrogen drugs represent a broad pharmacological group whose action is aimed at suppressing the effects of male sex hormones. Fundamentally, the mechanisms of action of this group are divided into two main pathways:
- Disruption of androgen hormone synthesis. This category includes enzyme system inhibitors that prevent the formation of active hormone forms (a prominent representative is finasteride).
- Blockade of androgen binding to receptors. These drugs compete with hormones for binding to specific cellular receptors, preventing already synthesized андрогены from realizing their biological effect.
Mechanism of action of finasteride
Finasteride (known by the trade name Proscar) is a classical inhibitor of androgen synthesis. Its pharmacodynamics is strictly linked to the 5-alpha-reductase enzyme.
The most important characteristic of the drug is its tissue specificity—its main action unfolds locally, directly within the tissues of the prostate gland.
The chain of pharmacological effects of finasteride is as follows:
- The drug binds to the 5-alpha-reductase enzyme and blocks its activity.
- As a result of this enzymatic blockade, the process of converting regular testosterone into its most active form—dihydrotestosterone—is severely disrupted.
- A sharp drop in the concentration of active dihydrotestosterone leads to a decrease in the hormonal stimulation of prostate cells.
- The reduction in cell proliferative activity naturally culminates in a decrease in the physical dimensions of the prostate gland and relief of urine outflow.
Alternative approach: alpha-adrenergic blockers
In addition to finasteride, which reduces prostate volume, drugs affecting smooth muscle tone are actively used in BPH therapy. Long-acting agents (e.g., doxazosin and terazosin) are considered drugs of choice in this niche. Prazosin and tamsulosin are also included in this group.
Mechanism of action in BPH:
- They selectively bind to $\alpha_{1A}$-adrenergic receptors.
- This receptor subtype is abundantly localized in the smooth muscles of the prostate gland itself, as well as in the prostatic urethra and the bladder neck area.
- Receptor blockade causes pronounced relaxation of the smooth musculature.
- This leads to a functional widening of the urethral lumen and a rapid improvement in urine outflow, without directly affecting testosterone secretion or prostate volume.
Briefly: answers to topical questions
Which drugs belong to the group of androgen receptor blockers?
Drugs that block androgen receptors include flutamide—a true hormone antagonist that blocks androgen receptors and is used in prostate cancer.
Finasteride is the "FINish" for 5-alpha-reductase. No enzyme—testosterone does not convert to dihydrotestosterone—the prostate stops growing.
Class and exam questions
What is the fundamental difference between the action of finasteride and doxazosin in BPH?
Finasteride reduces the physical volume of the prostate gland by blocking the synthesis of active androgens. Doxazosin, on the other hand, does not affect organ size, but merely relaxes the smooth musculature of the urethra and prostate by blocking alpha-1A adrenergic receptors, which widens the lumen of the urinary tract.
What is the main site of action of finasteride in the body?
The drug exhibits pronounced tissue specificity and acts predominantly in the prostate gland, where it inhibits the 5-alpha-reductase enzyme.
How exactly does finasteride stop prostate tissue growth?
By blocking 5-alpha-reductase, the drug disrupts the conversion of testosterone into active dihydrotestosterone. The absence of this stimulant reduces cell proliferation and leads to a decrease in gland size.
What else to study on this topic
- Comparative characteristics of long-acting alpha-adrenergic blockers (doxazosin, terazosin)
- Second group of antiandrogens: drugs that block receptor binding
- Distribution features of α1A-adrenergic receptors in the smooth musculature of the urogenital system
- Pharmacodynamics of tamsulosin and prazosin in the context of hyperplasia treatment
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